/Engine/Plugins/Developer/Concert/ConcertSync/ConcertSyncCore/Source/ConcertSyncCore/Public/ConcertDataStore.h
Searches the store for the specified key, if not found, adds a new key/value pair, otherwise, if the stored value type matches the initial value type, fetches the stored value. The store always sets the value version to 1 when the value is added.
The operation result. The possible result codes are:
[FConcertDataStoreResult](API\Plugins\ConcertSyncCore\FConcertDataStoreResult) FetchOrAdd ( const [FName](API\Runtime\Core\UObject\FName) & Key, const [FName](API\Runtime\Core\UObject\FName) & TypeName, const [FConcertSessionSerializedPayload](API\Plugins\Concert\FConcertSessionSerializedPayload) & SerializedValue )